Objective: To examine olfactory nerve.

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It is a first cranial and sensory nerve, and carries the sense of smell, Olfactory receptor (OR) proteins interact with odorant molecules in the nose, initiating a neuronal response that triggers the perception of smell. 1 Olfactory receptors are situated in olfactory membrane, that is modified mucous membrane lining the upper part of nostril, olfactory membrane has millions of OR, supported by sustenticular cells. the mucosa also contains mucus secreating bowmans gland, that continuously lines the olfactory mucosa and increase the action of odoriferous substances.

The mucosa also contains mucus secreating bowmans gland, that continuously lines the olfactory mucosa and increase the action of odoriferous substances. Olfactory receptor is a bipolar neuron, The OR cell is characterized by a distal process (the dendrite) which terminates in the olfactory passage as the olfactory rod. 2 The olfactory rod is provided with numerous cilia which are in number, and nonmyelinated. Axon of OR pierces the cribiform plate of ethmoid bone reaches olfactory bulb, here they synapse with dendrites of mitral cells these synapse form globular structures, called olfactory glomeruli. 3

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Axon of OR pierces the cribiform plate of ethmoid bone reaches olfactory bulb, here they synapse with dendrites of mitral cells these synapse form globular structures, called olfactory glomeruli. 3 The axons from the mitral cells, leave olfactory bulb and form olfactory tract, olfactory tract ends in the olfactory cortex, Odors reach the olfactory cleft via the orthonasal or retronasal route. Odors bind to receptor proteins on the OR neurons in the olfactory epithelium, which depolarizes the cell and sends the signal to the olfactory bulb. In the bulb the neuron synapses and propagates the signal centrally to primary and associational regions where the information is integrated with other sensory information. 4

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 Olfactory cells olfactory nerve Mitral cells in olfactory bulb Olfactory tract medial olfactory area Lateral olfactory area secondary olfactory tract limbic system and brain stem nuclei.

The odor is classified into aromatic (camphor,clove,bitter almonds) Burning odor (burning feathers and tobacco) Fragrant odor (fowers and perfumes) Garlic odor (garlic,onion,sulfer) Nauseating odor(decayed vegetables, feces) Repulsive odor (bed bugs) Ambrosial odor (musk)

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The minimum quantity of odorant in the air required to effect smell sentation is called threshold for smell.Odorants substances must be volatile, so they can be sniffed,they should be water soluble,so as to pass through the mucus to olfactory cells,and must be lipid soluble,so can penetrate lipid bilayer of olfactory cells to stimulate them. 5

Anosmia: loss of sense of smell, which can be temporary or permanent, temporary it occurs in common cold, sinusitis, and allergic conditions. Permanent occurs in head injury, tumors of anterior cranial fossa, and tuberculous meningitis, parkinsonism. Parosmia: it is the perversions of smell, offensive smells are perceived as pleasant smells and vice versa.It is psychogenic in origin. Hallucinations of smell,usually occur in temporal lobe epilepsy.

Hyposmia:Reduced ability to recognize and detect any odor,they are detected at highr concentrations,it is the most common disorder of smell. Hyperosmia:It is the increased or exagerrated olfactory sensation,also k/as olfactory hyperaesthesia,occurs in brain injury and neurotic conditions. 9

MATERIAL AND METHOD: This practical was performed at department of physiology LUMHS, with 20 students of 4 th semester, the procedure was explained to the volunteer, the nose was examined carefully with torch to exclude any pathology, volunteers were asked to close their eyes, one nostril of the volunteer was closed, common smells were presented to them like clove oil, they snuffed and identified the smell.

Boys girls yes yes Yes yes

Result: All the volunteers appreciated the smell of clove oil.

Discussion: The olfactory system has received considerable attention in recent years, because the simple sense organ the olfactory mucosa and its nerve can mediate discrimination of more than 10,000 different odors, which is due to presence of many different odorant receptors, and the glomeruli to which the receptor project function as feature detector. 6 The OR family is one of the largest known mammalian gene families, with around 900 genes in human. 7

Each glomerulus receives input from one type of olfactory receptors, however each OR respond to multiple odorants, and a single odorant is recognized by multiple receptor types, therefore each odorant produce different pattern of activated glomeruli and brain recognize the odor by pattern of glomerular activation, evidence is obtained in rats with optical imaging, that odorants that differ slightly in structure but smell differently activate different glomeruli. 8

 ABSTRACT :olfatory nerve is the first cranial and sensory nerve, the basic component of the olfactory nerve is the olfactory receptor that interact with the odorant molecules and initiate a cascade of reactions, for the perception of smell, the study to examine the olfactory nerve was conducted in department of physiology with 4 th semester students,20 in number,the odorant used was clove oil,the result shows that all students had intact sense of smell,this conclude the proper nerve conduction from mucosa to limbic system.

References: 1:loss of smell in the elderly,danis lafreniere,otolaryngeologic clinic of north america,feb,2009, :The glial cells in the layer of the bulb,j.r dourcette,26jan:2005:10:1002 3:electron microscope observation of olfactory mucosa A.J.lorezano, jcb,nov:25:2007 4:molecular development of olfactory nerve pathway,annuals of newyork acedemy of sciences;nov :differential effects of central and peripheral leisons of primary olfactory pathway,j verhagen,a.b oestriecher.11oct,2004:10:1002 6:prevalance of smell loss in parkinsons disease,a.haehner,s.bos veldt,aug2009:490:494 7.Screening test of olfaction,h.r briener,D.simmon 2009,rhinology The sense of smell: genomics of vertebrate odorant receptors JM Young, BJ Trask - Human Molecular Genetics, Oxford Univ Press 9.ganong,smell and taste,march 2001:

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